Cryogenics has been used for a long time as a means to relieve pain, and its beneficial effects on health and comfort are well-known.
The precursor to all existing cooling articles for pain relief is the ice bag, which however presents a major drawback, due to the fact that it offers a non-homogeneous cooling surface. In order to achieve some flexibility and adapt thereby to the form of the member or part to be cooled, the ice-bag has to be filled with ground ice, which requires that the bag can be opened. Although this allows a closer contact over the whole sore part than full solid ice in the ice-bag, ground ice, because it is made of small pieces, involves for the bag in which it is enclosed a non-homogeneous cooling contact with the surface to be cooled. Furthermore, as soon as the ice melts, the liquid water produced concentrates into the lower part of the bag, thus increasing the lack of homogeneity of the cooling effect.
During the last decades, new cooling articles have been s developed that show good thermal properties and better stability in their close contact with the surface to be cooled. In those commercially available a heat transfer medium made of an aqueous gel of propylene glycol and/or methylcellulose is used in the frozen state instead of ice. The gel is enclosed in an impervious film of organic material. Such is the case for instance for the cryogenic gel commercially known as a blue gel or the device known under the trademark Cold Hot 3M.
It has further been proposed to produce a higher cooling effect by permitting evaporation of water out of a highly absorbent medium swollen with water through an envelope made of a polyester fabric or some other permeable material. Examples for such devices are disclosed in Canadian patent application 2 135 966, the content of which is herein incorporated by reference. It can be understood therefrom that the medium enclosed in the non-waterproof envelope is in the form of a powder of polymer particles when dry, and it does not operate merely as a heat transfer medium. The enclosure is permeable to moisture as well as to water, and the article continues to produce a cooling refreshing effect during desorption of the water previously absorbed that escapes from the particles.
However, it is still desirable to enhance the properties of such articles and achieve a longer cooling effect. An article with a regularly homogeneous cooling effect which lasts over time can be useful in various industrial applications, for instance to preserve freshness of food or medecines, but proves especially useful in therapeutic applications, for removing extra heat from a member or part of the body to be treated.